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The genomic nucleotide sequences of the cloned agroinfectious genomes of three South African mastreviruses obtained from Zea mays, a Setaria sp., and Panicum maximum (designated MSV-Kom, MSV-Set, and PanSV-Kar respectively), were determined. Additionally, their relative infectivities and virulence were analysed in a range of differentially susceptible wheat, maize, and barley genotypes. MSV-Kom produced moderate to severe streak symptoms in all maize genotypes tested, but only moderate to very mild symptoms in the wheat and barley genotypes. MSV-Set infected only the susceptible to tolerant maize genotypes, but was generally more severe in the barley and wheat genotypes than MSV-Kom. PanSV-Kar was incapable of infecting any of the wheat and barley genotypes and only produced very mild symptoms on the three most sensitive maize genotypes. Genomic characteristics in common with related mastreviruses were identified. Phylogenetic analysis indicated that while MSV-Kom was closely related to previously sequenced MSV isolates, MSV-Set and PanSV-Kar represented distinctly novel strains of MSV and PanSV respectively. In the case of MSV-Set, this is the most distantly related MSV strain yet characterised.

A complete infectious genome of an isolate of maize streak subgroup 1 geminivirus from Reunion Island (MSV-R) was cloned and sequenced. Using an Agrobacterium tumefaciens Ti plasmid delivery system, the cloned 2.7 kb circular DNA was shown to be infectious in maize. The agroinfected virus could be transmitted by Cicadulina mbila, the most common vector species of MSV in Reunion. Analysis of open reading frames (ORFs) revealed seven potential coding regions including the 4 ORFs conserved in all geminiviruses infecting monocotyledonous plants, the 2 on the viral "+" strand (MP, CP), and the 2 on the complementary "-" strand (RepA, RepB). The nucleotide sequence of MSV-R was compared to previously determined sequence of three African clones from Nigeria (MSV-N), Kenya (MSV-K), and South Africa (MSV-S). More similarity was found between the African clones (97.0-97.3%) than between these and MSV-R (94.4-95.3%). Nucleotide substitutions were frequent in the large intergenic region, particularly in and around the most likely TATA box for the complementary sense genes, and in the 5' end of ORF V1. The comparison of the predicted peptide sequences of the proteins encoded by ORFs MP, RepA and RepB confirmed the higher similarity between the African clones (97.8-99.3%) than between these and MSV-R (95.1-97.1%). However the amino acid sequences of the protein encoded by ORF CP (capsid protein) were very conserved among all the 4 clones, suggesting a high selection pressure on this ORF.